1. Field of the Invention
The present invention generally relates to a semiconductor circuit apparatus having a converter for converting a power supply voltage and, particularly, to the operational control of the converter.
2. Description of Related Art
The recent semiconductor field has seen a decrease in power supply voltage as well as an increase in integration. Accordingly, an apparatus that operates with a low power supply voltage has been developed. Still, there are not a few apparatus that operate with a conventional power supply voltage, and it is often the case to combine apparatus with different power systems to configure a system. In this case, a booster that boosts a supply voltage may be used.
FIG. 8 shows the configuration of a booster of a related art (see Japanese Unexamined Patent Application Publication No. 2001-111397, for example). When an input signal Vφ is applied as a reference voltage Vss, transistors N4 and N5 are conductive to apply a voltage Vdd to a capacitor Cb, thereby charging the capacitor Cb. When the input signal Vφ turns a power supply voltage Vdd, a transistor P2 becomes conductive to apply a voltage of a sum of a switch terminal signal voltage Vin and the power supply voltage Vdd to the gates of switches (transistors) N0 and N1, so that the transistors N0 and N1 become conductive.
As described above, the booster of the related art always boosts the power supply voltage. It is thereby not compatible with the cases in need of selecting whether to boost a power supply voltage or not. The cases in need of such a selection involve a case that supplies a power supply voltage to a circuit during normal operation and supplies a boosted voltage from the power supply voltage to the circuit when a high-speed processing is needed. Those cases also involve a case that does not boost a voltage when the voltage of a power supply (e.g. charging battery) is sufficiently high and boosts the voltage when the voltage drops due to exhaust of the power supply or the like.
Those cases further involve a case that uses a single semiconductor apparatus with a plurality of different power supply voltages. If a semiconductor apparatus that includes a booster of a related art is designed on the assumption that a power supply voltage of 3.3V is supplied, it is unable to use the semiconductor apparatus with a power supply voltage of 5V. This is because the boosted voltage of a signal exceeds a withstand voltage of an operational circuit to cause the breakdown of the operational circuit. The above example is given by way of illustration only and is not to be construed to limit the scope of the invention.